CST8177 Ð Linux II let, CentOS VMs Todd Kelley kelleyt@algonquincollege.com CST8177Ð Todd Kelley 1 .CST8177 Linux Operating Systems II .Mon 22-Apr-13 12:00 14:00 CA105A,B,C Final Exam CST8177 Ð Todd Kelley 2 .let .CentOS VMs .group management .assignment05 3 TodayÕs Topics .let is not on tests in this course .let arg [arg...] .each arg is an arithmetic expression to evaluate .see ARITHMETIC EVALUATION of bash man page .shell variables are allowed with or without $ .arithmetic expressions can involve assignment of values to variables, where "=" is the basic assignment operator .examples: let a=1 echo $a let a=a+1 echo $a let (quickly, by request) CST8177 Ð Todd Kelley 4 .let seems great, why not use it? .because it's not as portable as the alternatives ."portable" means you can run your script unmodified on other systems, maybe running /bin/dash instead of /bin/bash, and it will work just as well .expr is "standard" and works everywhere .$((arith)) is what you would use if you don't want to use expr (and it's faster than expr) .x=0 .x=$(( x + 1 )) .x=$(( $x + 1 )) let (cont'd) CST8177 Ð Todd Kelley 5 .minimal install .when setting up a server, it's a "best practice" to start with the minimum and add only what you need .in our case, we will learn how to grow a system .add software .add disks .don't do any playing with or customization of or installations to your CentOS until you're told .Feel free to play with Linux, Linux GUIs, etc .do it in a clone of your CentOS VM .do it in a VM you create for playing (what, you haven't already done this?) CentOS VMs CST8177 Ð Todd Kelley 6 .http://teaching.idallen.com/cst8207/13w/notes/700_users_and_groups.html Group management CST8177 Ð Todd Kelley 7